1. Technical Field of the Invention
The present invention relates to novel dermocosmetic compositions comprising judiciously selected very low dosages of melatonin or analog thereof, having improved antioxidant activity, and which are particularly well-suited for improving or maintaining the appearance of human skin or the scalp.
2. Description of the Prior Art
The role of cellular oxidation in aging of the skin, both intrinsic and extrinsic aging, in particular photoinduced aging, is known to this art. Such aging of the skin is reflected in various clinical signs and conditions, in particular the appearance of fine lines and deep wrinkles which increase or are accentuated with age. Moreover, the appearance of the skin or the scalp deteriorates. The skin complexion is generally modified and diffuse irritations and occasionally telangiectasia may exist on certain areas of the skin. Another clinical sign of aging is the dry and coarse appearance of the skin, which is due essentially to more pronounced desquamation. Lastly, a loss of firmness and tonicity of the skin are observed, which, as for the wrinkles and fine lines, is at least partly explained by dermal and epidermal atrophy, as well as by a flattening out of the formation. It is thus observed that the clinical signs of aging of the skin result essentially from dysfunction of the principal biological mechanisms involved in the skin.
Preventing or treating aging of the skin, both intrinsic and extrinsic aging, and the clinical signs described above is essentially a matter of maintaining or improving the appearance of the skin or the scalp.
Various antioxidants capable of preventing or treating aging of the skin are described in the prior art, for example melatonin (EP-214,254).
Melatonin, or N-acetyl-5-methoxytryptamine, known especially for its activity on the circadian rhythm which regulates the production of hormones, is also described for its antioxidant activity (Reiter R. J., Verhandlung der Deutschen Zoologischen Gesellschaft, 87 (2), 195-204 (1994); Reiter R. J. et al., Neuroendocrinoll Letter, 15 (1-3), 103-113 (1993); Reiter R. J. et al., J. Pineal Res., 18 (1), 1-11 (1995)), in particular its anti-free-radical activity (Reiter R. J. et al., Brazilian Journal of Medical and Biological Research, 26 (22), 1141-1155 (1993)). Most of the studies of the antioxidant properties of melatonin relate to the oxidation phenomena associated with aging of the brain (Poeggeler B. et al., J. Pineal Res., 14 (4), 151-168 (1993); Cagnoli C. M. et al., J. Pineal Res., 18 (4), 222-226 (1995); Melchiorri D. et al., FASEB J., 9 (12), 1205-1210 (1995); Sewerynek E. et al., Neuroscience Letters, 195, (3), 203-205 (1995)).
Melatonin has also been described for dermocosmetic applications in order to improve the appearance of the skin (JP-61/221,104; WO 86/05093), or to protect the skin against the deleterious effects of irradiation with UV rays (EP-0,438,856; E. Bangha et al., Dermatology, 191, [2], 176 (1995)). It is recommended to use melatonin at concentrations of between 10.sup.-4 and 10% by weight relative to the total weight of the composition.
Thus, WO-86/05093 describes a cosmetic composition comprising melatonin to increase the skin sensitivity towards estrogens, in particular for the treatment of acne or the prevention of hair loss. The amounts of melatonin recommended in that application are generally between 10.sup.-4 % and more than 1% by weight relative to the total weight of the composition. The only two specific examples of compositions, a lotion for the treatment of acne and a solution for preventing hair loss, comprise 10% and 0.1% by weight of melatonin, respectively.
Similarly, EP-438,856, relating to compositions for protection of the skin against the deleterious effects of irradiation with UV rays, recommends amounts of melatonin of between 1% and 10% by weight for topical compositions, the only example of this type of composition comprising 10% melatonin.
JP-61/221,104 describes a cleansing milk comprising 10% melatonin in order to attenuate skin roughness. As regards the above two publications, the antioxidant action of melatonin is not mentioned for the effects studied.
The article by Bangha et al. (Dermatology, 191, [2], 176 (1995)) describes a gel containing melatonin which is capable of reducing the erythema induced by UV, probably on account of its anti-free-radical activity. The concentrations tested are 0.05, 0.1 and 0.5%, the authors recommending a concentration of 0.5%.